Event that fires when a url is confirmed as valid

Alright dudes... I have a problem that is looking for an answer more specific than the seemingly obvious solution.

I have a block of code that I want to execute directly after a url is 开发者_运维问答known to be valid. What I mean by 'valid' is that the program has checked to see if that filepath actually exists. This could be accomplished by a COMPLETE listener, because after all, a loader couldn't finish loading its content if the referenced file didn't exist, but I want it to happen before any of the bytes begin to get sucked in. I have also tried the HTTPS_STATUS event, with a conditional saying "if the status is this [some non-error status number], then run this block of code." This would have worked great, except that different environments produce different network codes, and some even can't distinguish between errors and non-errors, just returning 0's no matter what. Because of this, I can't write a conditional that works no matter what browser....

So, anyone got any ideas?!?!?!?!

If this doesn't work post your code.

myUrlLoader.addEventListener(Event.OPEN, openHandler);
//Dispatched when the download operation commences following a call to the URLLoader.load() method.